Wolfs Glass guard lifespan? Trying to replace with Nanolex

Does anyone know the life span of Wolfs Glass guard? It working fine on some surfaces but has lost its touch on others.

I am also looking to replace with nanolex glass sealant this time around but dont know if that is possible without removing the Wolfs. Any thoughts on if that is possible / how to do it since that are both nano products? Just a clay / polish?

Thanks!

Details. Glass Guard applied about 4 year ago but not on a daily driver. Only about 15,000 miles since application.